FIG. 3 is a cross-sectional view for illustrating conventional microphone structure.
Conventional microphones comprised case 3, diaphragm 1 that vibrates on receiving a sound pressure, back plate 2 disposed in parallel to diaphragm 1 with a fixed gap in between and having through-hole 2a, support 5 for holding diaphragm 1 and the periphery of back plate 2 with a fixed gap between them, mechanoelectric transducer 4 coupled to back plate 2, output terminal 6 for taking out an electric signal from mechanoelectric transducer 4 from inside case 3 to the outside, and hole 3a provided on the side of case 3 that directly faces diaphragm 1.
A description of the operation of the microphone will now be given below with reference to FIG. 3.
When pressure of a sound is transmitted to diaphragm 1 through hole 3a, the sound pressure is applied to the entire interior of the case that is not directly facing diaphragm 1 through two or more through holes 2a provided on back plate 2. As a result, diaphragm 1 vibrates and the fixed gap between diaphragm 1 and back plate 2 that is held parallel to diaphragm 1 changes thus causing a change in the electrostatic capacitance. The change in the capacitance is converted into an electric signal by mechanoelectric transducer 4 and put out to output terminal 6.
When pressure of an excessive sound is applied to diaphragm 1 of conventional microphones, diaphragm 1 that is deformed comes into contact with back plate 2. Consequently, conventional microphones suffered a problem in that the diaphragm became unable to vibrate at above a certain sound pressure level and distortion was caused.